Migrating from 1 server to a new server.

The link you provide states:

Prerequisites:
The Source and Target Primary servers must use the SAME hostname.

so you can not use the tool. I do not know a supported way to change the hostname without professional services.
Call support again and ask if a new version of the tool support that.

what version is your netbackup and what OS?

do you have any disk storage on the master server?

Keep in mind, install the same version of Netbackup in RHEL9, after that do a restore catalog Netbackup in the new server, keep hostname, version nbu, IP all the same and evertyhing is gonna be OK, check about some disk attached in Netbackup.

Ha, The tool cannot be used on source primary servers 10.2 and up. Add that to your comments for support.

I'm not asking about disc space on the master. I'm asking if you have an MSDP configuration on your master. I will assume that you do not have

admin_bkp007 is right. This is the supported procedure to migrate the primary server. If you try this path do not use any deduplication device for the catalog backup. use a basic disk. It will do thinks easer.

I do not use backup and restore for migrations. For big environments it is time consuming. In stead I use rsync.

The problem is that I have never tried to migrate a server bigger than 10.1.1 (the primaries with the new progress database).
I will write what my steps are to migrate a 10.1.1 server and you can try it. I do not think that you will have any problems.
After all, if the old server is there, the new one will not start.

• install OS (redhat 9) on the new server.
• use the same hostname as the old primary name (with FQDN if the old one is configured with FQDN).
  Check the first entry in the nbu configuration file for the name (cat /usr/openv/netbackup/bp.conf).
• use a temporary IP  and add an entry to the /etc/hosts file
• create the same users with the same groups and home directories for web services and Postgres.
• Install the same version of NetBackup.
• check that it is working ok (java or webui) and stop netbackup services.
• take a backup of the /usr/openv of the new server (mv or tar) and delete /usr/openv.
• use rsync to copy /usr/openv for old primary to the new one. Do not check the sync errors.
• if the environment is big and have many changes or the sync is slow, run it many times in order to minimize the copy time.
• When the sync finish, stop all netbackup services of the old primary server.
• run a last rsync. At that stage no sync errors must occur.
• swap the IPs of the servers (just to have the original server up in case you need something) and fix /etc/hosts
• start netbackup on the new server and do tests.
• If everything is okay, use the new server.

I had done this procedure several times, but as I told you, with netbackup up to 10.1.1. I do not expect to have problems with 10.3, but as always, do it at your own risk.

For the media server, just install a second media server (with new name) and retire the old one

No I had no problems. Some installations are more than 10 years old with many updates after the transfer.
before staring the sync, I suggest to install all EEBs you may have at your old server.

I have to state again that this procedure is not supported by veritas

This manual can be useful if for a reason you do not want to copy everything. I can not find it for newer versions. Check the "Deploying NetBackup primary servers with full catalog replication"
https://sort.veritas.com/DocPortal/pdf/39129704-160198727-1

To be in the safe side, catalog backup and recovery would be the better option here. Have basic disk stu to simplify the portability of the catalog backup image from source to the target system.

Use the same uid/gid for nbwebsvc/nbwebgrp and service user on the target system.

As you are looking to do this yourself, and probably without cost the Backup and Restore option should be the easiest as everyone else has stated..  Although you do need to have an OUTAGE to the backup environment from when you start the backup on the old master until after you have completed the restore on the new master.

Tranzman is a software solution that supports ALL NetBackup versions form 6.0 to 10.4 

It requires you to have DIFFERENT names for the old and new servers as both systems need to be on the network at the same time, and will need to be able to talk to clients/servers to test connectivity and ensure certificates are pushed/pulled before switch-over.  It works by reading catalog data from one working NetBackup environment and writing it into the other.   It keeps backup environments online for as long as possible with only a short outage needed at the time of switch-over.

Tranzman supports:-
migrations to/from clusters
between different operating systems (windows, hpux, solaris, aix, linux )
between different platforms (byo, flex, flexscale)
allows you to JUMP from old versions of NetBackup to Newer Versions without having to do upgrades.